This invention relates to semiconductor devices, and more particularly to semiconductor devices including an MOS field effect transistor having diffused regions for forming the source and drain.
High integration and miniaturization are significant objectives in the technical development of semiconductor devices, particularly semiconductor integrated circuit devices including MOS field effect transistors. Channel length is the most significant characteristic when attempting to miniaturize the device. A transistor or integrated circuit having a channel length of about 1 micron has been prepared experimentally, and integrated circuit devices having a channel length of about 3 microns are available in mass produced units. Most integrated circuit devices manufactured today have a channel length of about 5 microns.
As the channel length is reduced, a "short channel effect" occurs. The short channel effect is when there is a punch through the source and drain and a resulting drop in threshold voltage. In order to overcome the short channel effect, the following proposals have been made:
(1) Reduce the thickness of the gate film; PA1 (2) Heavily dope the substrate; and PA1 (3) Reduce the depth of diffusion at the source and drain diffused region.
Of the proposals for countering the shortened channel effect, the method of reducing the depth of diffusion by ion implantation at the source and drain regions is the most common. Additionally, methods have been proposed whereas As, Sb and the like having small diffusion coefficients are used as ion sources or utilizing boron or phosphorus to decrease the implantation energy and the amount of implantation at the diffused regions.
It has been found that as the diffusion depth is reduced or the amount of the diffusion source is decreased, metal penetrates into the diffused layers at the junction region. Specifically, the punch-through effect occurs at the junction region. Some penetration can be prevented by mixing silicon, copper, or the like, into an aluminum contact, but this does not prevent penetration completely when the depth of the diffusion region is reduced to about 0.2.mu. to 0.5.mu..
It has also been suggested that in order to prevent penetration of aluminum a chemically stable metal, such as platinum, be disposed or a polysilicon layer be disposed between the aluminum and the contact portion. When providing a barrier by disposing a chemically stable metal, such as platinum, adhesion between the barrier layer and the single-crystal silicon substrate or phosphorous silicate glass (PSG) film is not acceptable. The number of processing steps, such as vapor deposition and etching for forming the barrier layer, are also increased. Furthermore, there is a problem in that metals, such as platinum, do not etch uniformly. When utilizing a barrier layer of PSG the PSG barrier is apt to react with the aluminum thereby changing its properties. Additionally, when etching there is the possibility that a stepped portion may occur due to overhang. Furthermore, the binding characteristics are reduced. Accordingly, it would be desirable to provide a means to prevent penetration of the aluminum without increasing the processing steps.